Table 2.

Anatomical structures of the tear trough area and considerations for treatment

Structure	Description	Considerations for treatment with HA injection
Orbicularis oculi muscle 39	Forms a circle around the palpebral fissure and is divided into two parts: (a) orbital and (b) palpebral: in turn subdivided into pretarsal and preseptal	The region of the tear trough is located between the preseptal palpebral and orbital portion. In the transition between both, the muscle uses the orbitomalar ligament to insert itself into the bone, except for its innermost part, where it is inserted directly into it by means of small muscle fibers. It is not recommended to infiltrate this inner portion, as the fibers are so weak and fine that, even administering a submuscular injection, the HA could rise by positive pressure and compromise the lymphatic drainage of the region.
Malar septum 10 , 40	Fibrous tissue that extends from the orbital rim, behind the orbicularis oculi muscle, to the tarsus, where it is inserted joining the capsulopalpebral fascia.	Extremely important as this is a barrier impermeable to the diffusion of fluids. The area anterior/superficial to this has a higher risk of suffering edema in the event of overload of lymphatic vessels. Do not inject superficial to the septum.
Fat pads 41	There are three lower pads: medial, central, and lateral. They are found behind the septum.	In the management of tear trough deformity, the projection of the medial and central fat—which are separated by the inferior oblique muscle—is important.
Orbitomalar ligament	Originates at the level of the bone in the orbital rim and extends to the skin.	Where the inferior orbital rim is palpated is the upper limit of the area where we will inject the hyaluronic acid filler.
Preseptal‐preligamentous fat deposit 37	A small amount of fat, which is not always present, in front of the septum and the orbitomalar ligament.	When it exists, it induces a relief that may make it difficult to determine the position of the orbitomalar ligament. If we inject above the latter and at the level of this fat by mistake, we could perforate the septum and enter at intraorbital level.
SOOF (suborbicularis oculi fat) 42	Deposit of fatty tissue that is found between the orbitomalar ligament and the malar zygomatic.	It constitutes an ideal bed for the HA depots in the treatment of tear trough deformity, especially its highest part.
Zygomatic cutaneous ligament	Fibrous tissue that goes from the bone (between 0.2 and 1.1 mm below the inferior orbital rim) to the skin.	Defines the lower limit of the SOOF.
Vascular structures 43	The angular artery emerges below the orbicularis oculi muscle and along the inner canthus of the eye, medial to the area where the HA treatment should be given. The angular vein, which drains into the facial vein, runs alongside it. The lacrimal vessels in the vicinity of the tear trough are superficial to the orbicularis	Although they are not the branches that vascularize the lower eyelid region, the angular artery is the most important structure to consider, due to its anatomical proximity to the injection zone. Both this and the angular vein should be taken into consideration to avoid intravascular injection.
Nerve structures 39	The infraorbital nerve, which originates from the maxillary nerve (trigeminal branch), emerges through the infraorbital foramen to 0.6‐1 cm from the inferior orbital rim and at the level of the pupil. It is accompanied by the infraorbital artery and vein.	This nerve should be taken into account in the injection in the tear trough area since, although it is inferior and in many cases outside the injection area, poor practice on inserting the needle or cannula could damage it.
Lymphatic structures 37 , 44	The lymph vessels run at superficial level (dermis‐hypodermis). The outer third of the lower eyelid drains to the preauricular and parotid lymph nodes, while the inner two‐thirds drain to the submandibular lymph nodes.	It is extremely important to perform deep injections so as not alter the lymph drainage.